This invention relates to a process for producing foams based on alkali metal silicates by mixing the foam-forming components originally present in two separate pressurized containers and expelling the waterglass foam by means of a propellent gas liquefied under pressure at room temperature.
Various methods and various propellents and hardening agents for producing waterglass foams are described in the Patent literature. In this connection, a distinction has to be drawn between two fundamentally different procedures: on the one hand, chemical foaming where the propellent is formed for example by the decomposition of peroxides, preferably H.sub.2 O.sub.2, by metal powders or other reducing agents (DE-OS No. 22 27 640) or by the decomposition of carbides in aqueous solution (DE-OS No. 22 26 841); on the other hand, physical foaming where foaming is obtained by the injection of gases, for example air (DE-OS No. 20 39 736), or by heating (DE-OS No. 29 48 778).
Both procedures require elaborate machinery for metering and mixing several components (waterglass solution, hardener, propellent). Although they are suitable for the production of silicate foam products on an industrial scale, they are not really suitable for the production of silicate foams in situ, i.e. on site in the building industry for example. However, it is precisely in that field where silicate foams could be effectively used by virtue of their undisputed advantages over organic polymer materials (better temperature resistance without releasing toxic gases or smoke, non-inflammability, better processibility for the same insulation and construction properties). Above all, there is no known method for the simple production of in situ waterglass foams.